Tunnel kiln



J.. DANIELS TUNNEL KILN July 12, 1932.

Filed March 8, 1930 Z SheetsShe-et l J. DANIELS TUNNEL KILN Filed March'8, 1950 2. Sheets-Sheet 2 July 12, 1932..

Patented July 12, 1932 UNITED STATES PATENT OFF-VICE JOSEPH DANIELS, F ESSEN, GERMANY, ASSIGNOIB, BY MESNE ASSIGNMENTS, TO THE perature o? g Y by to be ensured, while outside this range a .KOPPERS COMPANY, or PITTSBURGH, PENNSYLVANIA, A

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CORPORATION OF DELA- TUNNEL I N Application filed March s, 1930, Serial No. 434,295, and in Gamay March '15, 1929.

1 In the operation of tunnelfkilns the procedure adopted for both the preheating and cooling zones is to extract the heating and cooling media in contra-flow to the material to be fired at the end of the zones opposite their point of entry. By following this method it is in the first instance neither possible to evenlyheat up or cool oil the top and bottom of the material under treatment, nor to accurately keep to the correct preheating and cooling curve. It is awell-known fact that firebricks, which constitute the chief product dealt with in tunnel kilns of this description, are extremely susceptible-to sudden changes in the temperature in a certain mean temperature zone of about 200-600 deg. cent., while they are less susceptible to sudden changes from these temperatures upwards to higher ones and conversely.

The problem, which is set with the subject of the application, will be best made clear in the following analysis, the object aimed at being to obtain LA functional separation of the firing zone, viz., a separation both to the side of the preheating zone and that of the cooling zone, this being attained without the necessity of interposing mechanical shutting-off elements between the zones, such as dampers and the like. The idea is to operate the kiln entirely on the regenerative principle, viz., to effect the heating solely with the heating media (gas and air) which is fired on the one side and the waste heat on the other side, that is to say, without any of the media or waste heat getting lost or requiring anything to be added. As a result, the possibility is' given of maintaining the high temperaturethroughout the length of the firing zone.

2; A positively controlled formation of the temperature curves, this againapplying to the preheating and cooling zone. Es"- pecially a radual rise of the rangeof temabout 200-600 deg. cent. is hereconcentration may and is to take-place."

3. The uniformity of the temperature throughout theentirecross se'ctionof the tunnel, this, of course, again applying chiefly to the higher regions in order to counteract cross section.

the irregularities in the temperature resulting from the buoyancy and one-sided travelling of the gases.

At any rate these three phenomena represent the first principles for the eflicicnt operation of atunnel kiln, especially if account has to-be taken of the susceptibility. of the material to be fired. v r V In the accompanying drawings Fig. l is a plan, and Fig.2 a corresponding cross section of a construction of the'cooling' zoneof a tunnel kiln, while Fig; 3 is a-plan, and Fig. 4 acorresponding cross section showing the corresponding construction of the preheat 111g zone. Fig. 5 is a longitudinal section, and Fig. 6 a cross section of a further con struction. Fig. 7 is a plan, and Fig. 8 a corresponding flow-sheet showing another posan elevation on a larger scale of the tunnel The cooling zone 10 of the tunnel kiln is traversed in thedirection of the arrow by the material to be fired coming from the firing zone 11. The cooling aims admitted under pressureto the delivery end 12 so that the entire cross section of the tunnel is kept filled withthe cooling media. The heated cooling air is extracted at the upper end of the cooling zone through the suction chambers 13 which so communicated with themainflueleadingto the chimney that the neighboring portion ll of the firing block is not affected. In order to extract the air by means of an ordinary suction fan andsimple ducts, and also to utie the extracted h g y-he ed r i ct yj o 'dry ng p rp ses and heilikcg co d ir j 1 is mixed with the'hot air prior to its, entry into the suction chamber l3,the cold air being introduced either under pressure by 7 means of a blower 1a, or by means of natural draught. v Fig. 2 shows the arrangement re: quired for the fmixingprocess. The hot air, which issues through akind of nozzle 15,- and" is capable of'being regulated by means of the brick 16, enters the suction chamber 13, together with the cold air entering fromthe annular passage 18, through the duct17,.the

hot air constituting a mixture already cooled down to a corresponding degree.

The introduction under pressure of the preheating medium for the preheating zone is effected as shown in Figs. 3 and 4t, fiue gas passing through the pressure burners 19, 19 into the distributing chambers 21 extending along the major portion of the length of the preheating zone, whence corresponding volumes of the heating media pass into the preheating z'one 20 through regulatable branches 22. The air is here likewise extracted at the end of the preheating zone through the connection 23, viz., atthe end of the kiln where the material to'b'e fired is admitted. In orderto provide additional means for regulating the temperature, the connections 22 are so constructed that cold air introduced through the duct 2% under pressure in a volume, which is, of course, likewiseregulatable by a damper 25," is admitted at the same time so that a preheating medium, whose volume and temperature is capable of regulation, is introduced into the preheating zone 20 at each of the connections 22. p

From the control curves plotted concurrently in Fig. 3 it will be seen that, starting from the point of the low temperature, larger volumes of cold air and smaller volmines of hot gases are admitted in order to put, the tunnel under pressure in this manner in the zone of. the lower temperature range and the range to which the material to be dealt with is more susceptible, that is to say, to render the volumes very large and to fill the tunnel space completely. Hence here again the range of the high temperature is driven back into the adjoining firing block or hotter preheating section, and a sudden rise in the temperature attained to the benefit of a long low-temperature zone. The large Volumes in the range ofthe critical and low temperatures heat up the inside of the material to be fired, with the result that assurance is given in a large measure of the material being heated up at the top and bottom as evenly as possible.

According tothe arrangement shown in Figs. 5 and 6, the heating process may be perfected still further as indicated in the following: To enable the temperature curve required in the preheating zone to be maintained to a high degree of accuracy at an equal level in. the upper and lower portions of'the various tunnel cross sections, the media,

which are forced in at every point of entry, are distributed along the higher regions of the tunnel, this being effected in such a manner that the'part media, which are conducted through the passages 26 leading upwards, are cooled down to a slightly lower temperature by admitting further volumes from the connections 27 and 28. As a result, these colder volumes, together with the media passing along the upper portion of the tunnel,ehave the same mixing temperature after being mixed as the media admitted at the car bot tom, these media having been correctly mixed from the outset to the temperature required for the tunnel section under consideration.

' In this mannerthe possibility is also given of operating short tunnel kilns at an equal temperature at all points at the top and bottom according to a specific preheating curve, and of controlling the preheating zone. A further advantage of this extension is gained in this case by the fact that the possibility is given of operating the preheating block 20 with a higher degree of suction at the entry without disturbing the exact course of the temperature curves, and running the risk of disturbing the firing zone on account of the high pressure, this being the case when the hot gases next to the firing zone pass over in part into the firing zone and cannot be induced'to pass to the end at which the cars are admitted for the purpose of being extracted.

arating a portion thereof, but of admitting the whole of the media into the arched portion and allowing it to enter at a slightly lowor temperature than actually required. By

following this method, thehot volumes flowing along the top are likewise cooled off, the descending media, which were admitted at the top, crossing the path of the hot volumes. As in the case referred to,'the gas volume" required to be extracted from the preheating zone at the end of the zone where the cars are admitted would increase to a very marked degree, and strong, under circumstances disturbing longitudinal currents, enter the preheating passage, the following method of working according to the modification shown in Figs. 7-10 is adopted: A gas volume corresponding to the preheating zone is with-- drawn at the end where the cars are admitted,

while the predetermined increase of the vol-v ume is only maintainedwithin the-critical temperature zone by recirculating a constant volume of flue gas at this point whose volume and temperature is regulated by admitting fresh air and discharging part of the flue gas to the roof or to the drying plant. It is expedient in this case, too, to extract this vol-V ume, which is requiredto be recirculated, by

means of centrally disposed tubes inserted in the stackedmaterial to be'fired and thus obtain a uniform distribution of the heat, whereby the recirculated gases are conducted back again in such a manner that-a transverse current is set up in the tunnel, such current-being fed againstthe material under treatment in the most uniformmannen;

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Hot gases are introduced into the preheating space 20, as shown in Fig. 7, through the medium of a preheating zone in the usual manner, these hot gases being extracted by means of a duct 30, which extends along the critical temperature zone, and the suction fan 31. The hot gases are withdrawn, as shown in Fi n 10, by centrally disposed tubes 33 which are introduced into the stacked material 32 and are capable of being put in communication with the duct 30 through the medium of a connection tube 34 with lifting and lowering motion by means of the lever mechanism 39 shown in Fig. 9, while this communication may be interrupted when the cars are to be moved forward. The air extracted in this manner by the suction fan 31 is, in the case referred to, conducted under the admission of cold outside air through the branch piece 35, or part of the volume delivered through the duct 36, into the bifurcated duct requires to be extracted at the end at which the cars are admitted through the suction openings 23, the gas volume being withdrawn throughout the length of the critical zone in such a manner that an exchange with the inside of the stacked material is ensured, while finally the method adopted of returning the gas volume sets up a transverse current permeating the entire block of material.

What I claim is: i

l. A tunnel kiln comprising, in combination: a firing chamber; a preheating chamber and a cooling chamber therefor at opposite ends thereof; independently regulable gas inlets distributed along the length of the preheating chamber for admission of heating gas thereto; independently regulable gas outlets distributed along the length of the cooling chamber for outflow of preheated cooling gas therefrom; and means for controlling the flow through said inlets and outlets so that they may be fed in graduation step-by-step toward the firing chamber; whereby the demarcation of the firing chamber from the preheating and cooling chambers maybe attained without the use of dampers and solely on pressure conditions created by said inlets and outlets, and a gradual rise and fall in the temperature and a local concentration of heat above the critical temperature range may be concurrently eifected in thecritical temperature zone of the bricks.

2. A tunnel kiln according to claim 1, and in which distributing passages extending alon the major portion of the length of the.

preheating chamber and having individual connections leading to said gas inlets on oplocal regulation of the gas volumes at the respective independent gas inlets. y

v 3. 'A tunnel kiln according to claim. 1, and

in which distributing passages extending along the major portion of the length of the preheating chamber and having individual connections leading to said gas inlets on opposite sides of the preheatingchamber are provided for admitting the gaseous preheating medium under pressure to the gas inlets, and in which air inlet means are provided for drawing or forcing cold air into the gas in lets along with the gaseous preheating medi- .um from the individual connections, whereby local regulation 'of temperature maybe, at the same time, combined with local regulation of the gas volume at the respective independent gas inlets, and in which further distributing passages having ports distributed along the walls of the preheating cham her from the-bottom up to the top of the tunnel arch are provided for eachof'said individual connections for: conducting and admitting part of the volume of the gaseous preheating medium to the preheating chame her at spaced intervals throughout the heightthereof.

t. A tunnel kiln according to claim '1, and in which distributing passages extending along the major portionof the length of the preheating chamber and having individual i connections leading .to said gas inlets on opposite sides of the preheating chamber are provided for admitting the gaseous preheated mediumunder pressure to the gas 7 lnlets, and 1n WhlCh'filI inletmeans are provided for drawing or forcing cold air into the gas inlets along withthe gaseous preheating medium from the individual con nections, whereby local regulation of temperature may be, at the same time, coml bined with local regulation" of the gas volumesat the respective independent gas" inlets, and in which further distributing passages having ports distributed along the walls of the preheating chamber from the bottom up to the top of the tunnel-arch are provided for each of the gas inlets for admitting part ofthe volume of the air and'gaseous preheating medium from each of the gas inlets to the preheating chamber as spaced intervals throughout the height thereof, and in which means are provided for mixing further air with the gas volumes that are admitted to the preheating chamber through the ports in upper portion thereof,

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whereby said gas volumes are so cooled down that after mixing with gaseous medium in the upper part of the chamber the mixture attains the same temperature as the tempera- 5 ture of the media admitted at the bottom 0 the chamber.

. 5. A tunnel kiln asclaimed in claim 1, and in which means are provided for recirculating a constant gas volume within the critical temperature zone of the preheating chamher and means are provided for admitting air to and drawingoil a part of the recirculating gas volume, whereby the remaining gas volume to be withdrawn from the car inlet to the preheating chamber and excessive longitudinal currents in the preheating chamber are limited.

6. A tunnel kiln as claimed in claim 1, and in which a suction ductis provided length- 7 wise above the arch of the preheating chamher, and in which centrally disposed vertical tubes are inserted in material stacked on cars in the chamber and adapted for connection with the suction duct for conveying part of the volume of preheating medium from the portion of the chamber at the soles of the cars to the suction duct, and a recircu lation flue is provided for recirculating the gaseous preheating medium from the suction duct back to the critical temperature zone of the preheating chamber.

- 7 A tunnel kiln as claimed in claim 1, and in which is provided a suction duct extending lengthwise above the preheating chamber, vertical tubes inserted in material stacked in cars in the chamber and adapted for connection with the suction duct for conveying part of the volume of gaseous preheating medium from the lower portion of the chamber to the suction duct, ports in the arch of the tunnel of the preheating chamber for admitting gas thereinto and a recirculation flue for recirculating gaseous preheating medium from the suction duct to the ports, whereby gas currents of recirculated gas are set up transversely of the tunnel preheating chamber.

8. A tunnel kiln as claimed in claim 1, and in which means are provided for withdrawing the reheated cooling medium from the outlets rom the cooling chamber by suction, and air supply means are provided adjacent the outlets for admitting cold air thereto at the point of suction on the highly heated cooling medium passing therefrom; whereby, on the one hand, the medium may be withdrawn by an ordinary suctionxfan, and, on the other hand, the suction extracted mixture may be directly used for drying pur- I poses and the like.

In witness whereof I aflix my signature.

JOSEPH DANIELS. 

